Data connection for head unit, leaving phone in my pocket

A

AC Question

I'd like to enter my car, leave my phone in my pocket, and get AA apps on my DoubleDin touch display -- WITH a supporting data connection.

As far as I can tell, this isn't yet possible. Is that accurate?
Option A - "brains on the phone") Proxy my phone's UI to my DD display: No joy, still requires a USB cable despite early 2016 reports that a wireless version was Coming Soon...
Option B - "brains on the head unit") Run Android (Auto or otherwise) on a tablet-like DoubleDIN head unit: No joy, because there'd be no data connection while on the road, unless I manually turn my phone into a Wifi Hotspot (a battery drain, so infeasible to leave it on all the time).

Is there a solution I'm missing here?
For instance, if I left Bluetooth enabled for my phone, can that wake up (and subsequently shut down) the Wifi Hotspot for Option B?

Reliable, supported solutions only, please. I'm not interested in tinkering.
-D